The invention is in the field of electronic reproduction technology and is directed to a method for engraving rastered printing cylinders, particularly for rotor gravure, with an engraving element in an electronic engraving machine.
When engraving rastered printing cylinders in an electronic engraving machine, an engraving element that, for example, comprises an engraving stylus as a cutting tool moves along a rotating printing cylinder in the axial direction continuously or step-by-step. The engraving stylus controlled by an engraving signal cuts a sequence of depressions arranged in a raster, referred to below as cups, into the generated surface of the printing cylinder. The engraving signal is formed from the superimposition of an image signal representing the hues between "black" and "white" with a periodic raster signal. Together with the circumferential speed of the printing cylinder and the axial feed speed of the engraving element, the raster signal defines the geometry of the engraved raster. Whereas the periodic raster signal effects a vibrating lifting motion of the engraving stylus, the image signal--corresponding to the hues to be reproduced--controls the depths of the cups engraved into the generated surface of the printing cylinder.
Such an engraving machine for engraving printing cylinders is disclosed, for example, by WO-A-94/19900. This is a matter of a method for calibrating an engraving signal, whereby cups are engraved, the geometric actual dimensions of the engraved cups are measured, and whereby setting values are determined from the comparison of the measured actual value dimensions to predetermined rated dimensions, the engraving signal values for selected gradations being corrected with the setting values such that the actual gradations in fact engraved in the form of cups correspond to the rated gradations defined by the image signal values.
GB-A-1407487 discloses another engraving machine for engraving printing cylinders. This is a matter of a method for engraving a printing page composed of a plurality of image and text parts compiled according to a layout plan, whereby the engraving data required for engraving the printing page are compiled from the engraving data of the individual image and text parts according to the layout plan to form overall engraving lines before the engraving and are stored, and whereby the compiled engraving data of the overall engraving lines are read out in the engraving and supplied to the engraving element.
In manufacturing printing forms, particularly for packaging printing, sequential, i.e. successively sequencing engravings' must often be produced with the same or with different engraving parameters such as, for example, the raster parameters of screen angle and raster width. Examples of sequential engraving are the re-engraving of areas within an initial engraving or multiple engravings (copies) of half-tone images and line information or, respectively, bar codes in the axial direction. The sequential engravings can occur on a printing cylinder or on a plurality of printing cylinders having the same or different diameters.
Due to the function modes of traditional engraving machines, such sequential engravings with different engraving parameters on one printing cylinder or on a plurality of printing cylinders with, potentially, different diameters' cannot he automatically implemented in one pass, for example without intervention of an operator in a night shift, which is disadvantageous.